The related art, for example the document US 2010/0245777 A1, discloses lighting devices for projection applications which include a disk-shaped phosphor wheel having one or more phosphors. In this case, said lighting devices include an excitation radiation source, which excites the phosphor to emit light having a different wavelength than the excitation radiation wavelength (wavelength conversion of the excitation radiation by means of phosphor). The phosphors are usually arranged successively in the direction of rotation on one side of the phosphor wheel, such that the light (converted light) emitted by the respective phosphor is generated temporally sequentially and fed to the imaging system.
Lasers, for example laser diodes, are preferably used as the excitation radiation source. In this case, the technology is also known by the designation LARP (“Laser Activated Remote Phosphor”).
The document CN 102385233 A discloses a lighting device for a projector including an excitation laser, a phosphor wheel for the wavelength conversion of the excitation laser light into conversion light, and a filter wheel, for spectrally filtering the conversion light. The excitation laser light is directed onto the phosphor wheel with the aid of a dichroic mirror. The conversion light reflected back from the phosphor wheel passes through the dichroic mirror and impinges on the filter wheel. The excitation laser light can pass through a transparency segment in the phosphor wheel and is fed to the dichroic mirror via a wraparound loop. The dichroic mirror reflects the excitation laser light to the filter wheel. The filter wheel and the phosphor wheel are arranged on a common axis and thus rotate synchronously at the same speed. In this way, the conversion light generated sequentially by a phosphor segment of the phosphor wheel is spectrally filtered by an assigned filter segment of the filter wheel.
The document EP 2 530 520 A1 discloses a lighting device for use in a projector. The lighting device includes a phosphor wheel coated on one side, said phosphor wheel consisting of a transparent circular-disk-shaped carrier material, three quarters of the front side of which is coated with various phosphors. The uncoated quarter serves as a transparent segment. The laser radiation is radiated through said transparent segment and deflected via mirrors onto the rear side of the phosphor wheel, where the laser beam passes through the transparent carrier material and excites a blue phosphor—applied behind the latter on the front side in one quarter segment—to emit blue light. The blue phosphor conversion therefore takes place in transmission. The other two quarter segments are coated with green phosphor. The green phosphor conversion takes place here in reflection. However, a reflection layer is required between each phosphor layer and the transparent carrier material in order that the light converted by the respective phosphor can be emitted from the front side and combined in a common direction. Otherwise, part of the converted light would be lost through the transparent substrate in the opposite direction. At least for the blue phosphor segment (transmission mode), the reflection layer must additionally be transmissive to the laser radiation. Red light from a separate light emitting diode (LED) is admixed for the red light channel.
The document US 2012/0243205 A1 likewise discloses a lighting device for use in a projector. In one variant, a phosphor wheel runs in a slot in a curved reflector, specifically through the focal point thereof. The phosphor wheel has on both sides, i.e. both on one side and on the other side of the usually circular carrier disk of the phosphor wheel, a region provided with phosphor. The light intensity of the arrangement is intended to be increased as a result. However, two separate excitation radiation sources are provided for this purpose, wherein each of the two sides of the phosphor wheel is irradiated through corresponding openings in the reflector in the region of the focal point with the aid of a respective excitation radiation source.